1. Field of the Invention
The present invention relates to a radio communication apparatus for transmitting signals between an outdoor unit and an indoor unit which are connected through a cable and, more particularly, to a radio communication apparatus capable of adjusting the level of a reception signal by inputting reception system installation parameters.
2. Description of the Prior Art
Reception signal level adjustment generally adopted in a very small aperture terminal (VSAT) or the like in a conventional radio communication apparatus is performed as follows. The demodulator of an outdoor unit compares a demodulated reception signal with the reference signal set in the modulator. The input level of the reception signal at the input point of an indoor unit is then controlled such that the difference between the reception signal and the reference signal falls within a predetermined range.
The signal output from the demodulator is input to a CPU. The signal is then coded by using a predetermined conversion table and output in a D/A format. The signal output from the CPU is converted into a control signal for a level adjustment PIN diode by the D/A converter. The attenuation amount of the PIN diode is changed in accordance with this signal to adjust the reception signal level. Since the level adjustment PIN diode is located at the input point of the indoor unit, the reception signal level of the indoor unit is kept constant.
The following problem, however, is posed in the conventional radio communication apparatus.
In reception signal level adjustment generally adopted in a very small aperture terminal (VSAT) or the like, since one level adjustment circuit is used to eliminate a fixed level difference based on the installation parameters associated with the indoor unit and variation level difference due to rainfall attenuation or inter-terminal deviation, an automatic gain adjustment circuit needs to have an excessive dynamic range. As a result, the subsequent circuit arrangement becomes complicated.
The present invention has been made in consideration of the above situation in the prior art, and has as its object to provide a radio communication apparatus which can reduce the dynamic range of an automatic gain adjustment circuit with respect to a variation level difference due to rainfall attenuation or an inter-terminal deviation by eliminating a fixed level difference, and can simplify the circuit arrangement on the subsequent stage.
In order to achieve the above object, according to the main aspect of the present invention, there is provided a radio communication apparatus for transmitting a signal between an outdoor unit and an indoor unit which are connected to each other through a cable, comprising a variable level adjustment circuit in the indoor unit, wherein a fixed level difference of a reception signal due to installation parameters of a reception system is eliminated, and the reception signal is adjusted to make a reception signal level become equal to a predetermined standard input level.
According to the first auxiliary aspect of the present invention, the indoor unit comprises an operation panel for setting/inputting the installation parameters.
According to the second auxiliary aspect of the present invention, the indoor unit in the principal aspect comprises a CPU for calculating a fixed level difference of a reception signal in accordance with the installation parameters and outputting a control signal for adjusting the reception signal in the variable level adjustment circuit.
According to the third auxiliary aspect of the present invention, the CPU in the second auxiliary aspect calculates the fixed level difference of the reception signal at an indoor unit input point in accordance with the installation parameters.
According to the fourth auxiliary aspect of the present invention, the CPU in the second auxiliary aspect is connected to a table in which attenuation and amplification amounts are set in advance with respect to the installation parameters.
According to the first auxiliary aspect, in the principal aspect and the respective auxiliary aspects, the installation parameters include at least an antenna diameter of an antenna connected to the outdoor unit, a type of the outdoor unit, and a type and length of the cable.
In the radio communication apparatus of the present invention for transmitting a signal between an outdoor unit and an indoor unit which are connected to each other through a cable, the indoor unit includes a variable level adjustment circuit. In this apparatus, a fixed level difference of a reception signal due to installation parameters of a reception system is eliminated, and the reception signal is adjusted to make a reception signal level become equal to a predetermined standard input level. With this arrangement, the dynamic range of the automatic gain adjustment circuit with respect to a variation level difference caused by rainfall attenuation, an inter-terminal deviation, or the like can be reduced, and both the arrangement of the automatic gain adjustment circuit itself and the subsequent circuit arrangement can be simplified.
The indoor unit comprises an operation panel for setting/inputting the installation parameters. Therefore, the installation parameters can be easily set, and the circuit arrangement can be simplified.
The indoor unit comprises a CPU for calculating a fixed level difference of a reception signal in accordance with the installation parameters and outputting a control signal for adjusting the reception signal in the variable level adjustment circuit. With a simple arrangement, therefore, a control signal for adjusting a reception signal can be output, and the circuit arrangement can be simplified.
The CPU calculates the fixed level difference of the reception signal at an indoor unit input point in accordance with the installation parameters. With this operation, the fixed level difference of the reception signal can be accurately calculated, and the circuit arrangement can be simplified.
The CPU is connected to a table in which attenuation and amplification amounts are set in advance with respect to the installation parameters. With this arrangement, the fixed level difference of the reception signal can be accurately calculated, and the circuit arrangement can be simplified.
The installation parameters include at least an antenna diameter of an antenna connected to the outdoor unit, a type of the outdoor unit, and a type and length of the cable. Therefore, the installation parameters can be set in accordance with the radio communication apparatus, and the circuit arrangement can be simplified.